CVGHM reported that seismicity from Batur decreased from 1 June to 17 November and fumarolic plumes rose from the crater. On 19 November the Alert level was lowered to Normal, or 1 (on a scale of 1-4).

Batur stratovolcano sits at the E end of the island of Bali amid nested calderas (figure 4) and rises 686 m above the surface of an intra-caldera lake of the same name (Sutawidjaja, 2009). The entire complex remained non-eruptive through at least mid-2011 as it has for at least a decade (since a moderate eruption in 1974 and a series of smaller eruptions in the 1990s ceasing in about 2000). Local authorities reported that, following some variable seismicity during 2009-2010, starting 19 June 2011 residents smelled sulfurous gas and saw many dead fish floating on the lake's surface. The kill took place in the volcano's caldera lake but in the absence of visible eruptive activity and without anomalous geophysical perturbations.

Figure 4. Physiographic map of the island of Bali highlighting Batur caldera. The topographic high in the N-central caldera is Batur stratovolcano (summit elevation, 1,717 m). The lake (not delineated) lies along the caldera's SE side. Taken from Sutawidjaja (2009).

Our previous report on Batur (BGVN 34:11) had noted increased seismicity from September to 7 November 2009. Since that report, the Center of Volcanology and Geological Hazard Mitigation (CVGHM) has reported that seismicity from Batur decreased from 1 June to 17 November 2010 and fumarolic plumes rose from the crater. On 19 November the Alert level was lowered to Normal, or 1.

Investigation of thousands of dead fish. CVGHM scientists visited Lake Batur (figure 5) to learn more about the incident. They learned that residents of lakeside villages first observed lake water discoloration and acrid (like sulfur) odors on the morning of 19 June 2011. A greenish-white discoloration first emerged in spots, but these spots soon connected and spread. The residents had seen a slick on the water surface spread from the E-central lake shore towards the S (from Toya Bungkah to Buahan, figure 6). In conjunction with these changes in color, thousands of dead fish were found at the surface of the lake (figure 7).

Figure 5. Photo of Lake Batur with two farmers for scale. The tops of fish cages (kerambah) can be seen in the lake water. Note steep caldera wall in background. Photo taken from allvoices.com. (Photographer unknown and other details undisclosed.)

Figure 6. Map showing location of Lake Batur, with the locations of the greenish-white water seen near the coast (shaded). The lake is 7.7 km in the long dimension and has a surface area of 16 km2. Courtesy of CVGHM.

Figure 7. Photo of dead fish floating on the surface of Lake Batur associated with the fish kill of 2011. Thousand of fish died, many near the village of Toya Bungkah. Undated photo taken from indosurflife.com.

The translated report contained this important passage. "According to information from a resident (Made Yuni, age 59), the change in color of the lake water, consisting of patches of whitish green, is a yearly event, although [typically] small in scale and not causing the death of fish. The change in color of the lake water occurs during the change of seasons (i.e. the transition), between the wet and dry parts of the year when there is a stiff wind from the S. The incident of the lake water changing color and the death of the fish on 19 June 2011 occurred about two weeks into the dry season. The death of fish in Batur on the present scale happened before, in 1995."

Scientists conducted an examination during 21-22 June 2011. They also had pre-event temperature and pH for multiple sites on the lake going back at least several months. At the time of the visit, all residual odors had dispersed. Results of ambient gas measurements showed no traces of anomalous carbon monoxide, carbon dioxide, methane, or hydrogen sulfide. The lake temperature was found to be 15°C, which is considered normal. pH levels in the lake were found to be constant with other measurements taken in normal times as well. No increase in volcanic earthquakes were reported before or after the fish kill (the pattern of earthquakes was constant at typical background, 1 event/day). The colors seen were attributed to both warm water welling up (springs at Toya Bungkah) but also at places where such springs are absent.

On 20 June the water by the village of Seked returned to its normal color. Late in 21 June the water by the other villages involved returned to its normal color. Scientists found neither dead weeds or algae nor gas bubbles associated with the fish kill.

Cause of fish kill. Scientists from CVGHM found no evidence to conclude the fish kill was volcanically triggered nor did they mention it portending eruptive activity. Rather, the scientists noted the comparatively high diurnal-temperature difference during the onset of the dry season. As a result of these temperature differences, the lake water developed currents, which carried mud from the lake bottom to the surface. This was thought to correspond to the observed odors ('muddy smells') and color changes on the lake surface. In a broad sense, the currents and mud were thought to upset the lake's ecological balance in a manner toxic to the fish.

Residents were advised to not consume dead fish from the incident, but fish that had survived were still considered fit for human consumption.

Impactof fish kill. Many inhabitants around Lake Batur are fisherman by trade and it is estimated that the fish kill resulted in losses up to billions of Rupiah (1 billion Rupiah currently equivalent to ~ 120,000 US Dollars). The water of Lake Batur is also irrigated into surrounding farms. There is no official documentation on whether or not the recent events at Lake Batur have affected the neighboring agriculture.

Weekly Reports - Index

CVGHM reported that seismicity from Batur decreased from 1 June to 17 November and fumarolic plumes rose from the crater. On 19 November the Alert level was lowered to Normal, or 1 (on a scale of 1-4).

CVGHM reported increased seismicity from Batur from September to 7 November and a significant increase in the number of volcanic earthquakes on 8 November. The Alert Level was raised to 2 (on a scale of 1-4).

VSI reported that there were no major changes visible at Batur during 9-15 April. Thin steam plumes continued to rise above the volcano's crater. Seismographs recorded no shallow volcanic earthquakes, two deep volcanic earthquakes, two small explosion earthquakes, and 17 tectonic earthquakes. The volcano remained at Alert Level 2 (on a scale of 1-4).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

A thin white plume rose 2-10 m from the solfatara field in the N wall of the crater. Gases emerged with a weak hissing sound and had temperatures of 40-80°C in 27° air. Other solfataras emitted 2-5-m white plumes at 90-95°C. Seismic stations recorded one local and 26 distant tectonic events, and one volcanic earthquake in November.

First significant eruptive activity in 18 years leads to ashfall 6 km WSW of the summit

Beginning on 4 August, the daily number of A-type volcanic earthquakes increased to 14; two days later 125 events were registered. An eruption on 7 August from the E part of the summit, Batur Crater III, caused ashfall as far as ~6 km WSW (figure 1). Ash covered Kintamani on the caldera rim, one of Bali's famous tourist attractions. Incandescent lava fragments and black smoke were ejected to heights of 300 m. None of the larger lava fragments fell outside of the active crater. News reports indicated that the eruption generated 960 explosions through 11 August. Volcanic tremor recorded by the VSI on 13 August had a maximum amplitude of 4.5 mm, but was increasing. By 14 August, when lava reached the surface, the tremor amplitude was 23 mm.

Figure 1. Map of the Batur caldera, showing hazard zones, selected towns, and extent of ashfall from the eruption that began on 7 Aug 1994. The inner caldera is not shown, but includes most of danger zones I and II. Courtesy of VSI.

As of 18 August, no evacuations from the area around the . . . volcano had taken place. About 180,000 people live in Bangli Regency, but only ~500 live in what a spokesman called the "critical region." Batur was declared off-limits for climbers on 7 August, and local villagers were put on alert. An official at a monitoring center said tourists who evaded guards and climbed the mountain were taking large risks. According to press reports, the eruptions have not reduced the number of visitors to the popular resort island; Batur's crater attracts ~300 people every day. Many observe the volcanic activity from Kintamani, on the crater rim (figure 1).

An . . . eruption . . . on 7 August . . . marked the first significant eruptive activity in 18 years. According to a 12 August Reuters news report, during 7-11 August Batur "spewed glowing ash and smoke more than 600 times." The Reuters report noted that a spokesman for the local governor's office said "the threat of a major volcanic blast on Indonesia's resort island of Bali appeared to lessen on Friday [12 August] after Mount Batur's activity slowed." The news report also quoted Wimpy Tjetjep (VSI): "The probability that there will be a big and destructive eruption is small."

During the first week of July, Batur continuously emitted a gray plume 25-300 m above the crater. Observers saw incandescent material frequently ejected. Two episodes of tremor with amplitudes of 0.3-24 mm were recorded.

During the week of 9-15 March, white ash plumes rose 10-100 m above the crater. Booming noises were heard six times, and volcanic earthquakes increased drastically compared to the previous week (table 1). It was later determined that an ash eruption had begun on 15 March, sending bluish-white plumes 10-50 m high. On 17 March, two relatively recent craters merged when a connecting ridge collapsed as a result of earthquakes and small eruptions.

Table 1. Weekly seismicity recorded at Batur, March-July 1999. Types of events include volcanic A-type, volcanic B-type, tectonic, explosion earthquakes, and ash emissions (small explosion earthquakes). No data were available for the period 30 March-19 April. Maximum explosion amplitudes were reported as 2-26 mm during May; more typical, smaller amplitudes were 1.5-24 mm during May-July. Courtesy of VSI.

Volcanic activity was dominated by emission events (small explosions) during the week of 23-29 March; the eruption plume was white-blue in color, rising 10-100 m above crater rim. Booming noises were heard three times on 22 March, but no glow was observed. Reports are not available for most of April, but during late April through the middle of May the seismic record was dominated by explosion events. Ash plumes, described as "white" or "white-bluish" were observed rising 50-100 m above the crater. Neither explosion sounds nor glow was observed.

Six explosions on 17 May ejected materials that fell around the crater. Another explosion on 25 May was accompanied by incandescent ejections that fell around the crater. Explosion sounds were heard on 17 occasions during the week of 25-31 May. "White ash emissions" rose only to 25 m during 1-14 June, but varied between 10 and 100 m the rest of the month. Similar activity continued through mid-July, and a variable rumbling noise was heard the week of 13-19 July.

Intermittent explosive activity has continued since July 1999 (BGVN 24:06). The following report covers the periods of August-September 1999, February-June 2000, and August-September 2000. Reports were not available for the interim periods. However, there was no activity on 20 July 2000 (figure 2) when participants attending the IAVCEI General Assembly visited the caldera (see Sutawidjaja, 2000).

Figure 2. Photograph of the active cone at Batur, 20 July 2000. View is looking NE from Penelokan on the caldera rim. Courtesy of Edward Venzke, SI.

In August 1999, Batur Post Observatory (BPO) observed frequent ash emissions and small explosions. Ash eruptions varied in height from 5 to 150 m above the volcano's crater rim. Some explosive events were accompanied by ejection of lava; the material rose 10-25 m, and incandescence could be observed at night. Explosion earthquakes dominated seismicity, which increased relative to the previous month. Frequent rumbling of varying intensity could be heard in the vicinity of Batur. During September, ash ejection increased in height, ranging from 25 to 250 m. Incandescent material continued to erupt from the crater. Seismicity continued to increase; seismographs recorded explosion earthquakes with amplitudes of 2-28 mm.

Ash emission, lava ejection, and mild explosions occurred during February 2000. Ash rose 25-250 m above the summit. Ejection of molten material accompanied some explosions. Rumbling could be heard frequently around the volcano. Overall seismicity was lower than in September 1999; fewer explosion earthquakes and slightly more shallow volcanic (B-type) earthquakes occurred. In the middle of the month, a gray ash plume rose up to 300 m above the summit. Ejected material fell up to 50 m from the center of the crater. By the end of February, ash emissions rose 10-50 m above the summit. Explosion frequency and intensity decreased. Low-density, white ash-and-gas emissions rose up to 75 m in early March. In mid-March the ash plume rose 10-25 m. Audible rumbling ceased, and seismicity decreased substantially.

On 22-23 March, a large explosion issued from the crater; ejecta were sent 200 m above the rim and rained back down within the crater. Seismicity increased along with the frequency of explosion earthquakes. Explosions and ash emissions continued into April, when ash and explosion debris reached up to 300 m in height, and rumbling resumed. Seismicity decreased by the end of the month. By early May, emission had decreased to a low-density, white ash-and-gas plume and rose 5-25 m above the crater rim. Rumbling ceased. Similar emissions and seismicity remained through the end of June. During August-September, a low-density, white plume rose up to 10 m above the crater rim, and seismicity maintained relatively low levels.

White, thin plume to 10 m above crater rim during March and April 2001

During March and April 2001, a thin-white plume was observed reaching up to 10 m above the crater rim at Batur. During January through April 2001 unspecified categories of monthly earthquakes numbered 6, 10, 20, and 6, respectively; their depths were 2-5 km. Some further details on specific types of March-April earthquakes appear in table 2. Based on these data, the Volcanological Survey of Indonesia (VSI) lowered the Alert Level from 2 to 1 (on a scale of 1-4) in early May. No further activity has been reported as of September 2001.

Table 2. Seismic activity registered at Batur during March and April 2001. Courtesy of VSI.

The Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that seismicity at Batur (figure 3) increased from September 2009 to 7 November 2009, and the number of earthquakes increased significantly on 8 November (table 3). During this period, sulfurous plumes were ejected from the craters. The Alert Level was raised to 2 (on a scale of 1-4). This seismic activity was the first noted at Batur since 2001, when a series of mild earthquakes occurred (BGVN 26:09).

Figure 3. Panorama of Batur caldera showing the ~ 7-km-long lake in the SE part of the caldera along with the cental topographic high composed of intracaldera cones. Copyrighted photo courtesy of "tropicaLiving" taken on 9 April 2008.

Table 3. Number of different types of earthquakes registered at Batur between September 2009 and 8 November 2009. *Through 1830 local time on 8 November. Data from CVGHM.

Batur stratovolcano sits at the E end of the island of Bali amid nested calderas (figure 4) and rises 686 m above the surface of an intra-caldera lake of the same name (Sutawidjaja, 2009). The entire complex remained non-eruptive through at least mid-2011 as it has for at least a decade (since a moderate eruption in 1974 and a series of smaller eruptions in the 1990s ceasing in about 2000). Local authorities reported that, following some variable seismicity during 2009-2010, starting 19 June 2011 residents smelled sulfurous gas and saw many dead fish floating on the lake's surface. The kill took place in the volcano's caldera lake but in the absence of visible eruptive activity and without anomalous geophysical perturbations.

Figure 4. Physiographic map of the island of Bali highlighting Batur caldera. The topographic high in the N-central caldera is Batur stratovolcano (summit elevation, 1,717 m). The lake (not delineated) lies along the caldera's SE side. Taken from Sutawidjaja (2009).

Our previous report on Batur (BGVN 34:11) had noted increased seismicity from September to 7 November 2009. Since that report, the Center of Volcanology and Geological Hazard Mitigation (CVGHM) has reported that seismicity from Batur decreased from 1 June to 17 November 2010 and fumarolic plumes rose from the crater. On 19 November the Alert level was lowered to Normal, or 1.

Investigation of thousands of dead fish. CVGHM scientists visited Lake Batur (figure 5) to learn more about the incident. They learned that residents of lakeside villages first observed lake water discoloration and acrid (like sulfur) odors on the morning of 19 June 2011. A greenish-white discoloration first emerged in spots, but these spots soon connected and spread. The residents had seen a slick on the water surface spread from the E-central lake shore towards the S (from Toya Bungkah to Buahan, figure 6). In conjunction with these changes in color, thousands of dead fish were found at the surface of the lake (figure 7).

Figure 5. Photo of Lake Batur with two farmers for scale. The tops of fish cages (kerambah) can be seen in the lake water. Note steep caldera wall in background. Photo taken from allvoices.com. (Photographer unknown and other details undisclosed.)

Figure 6. Map showing location of Lake Batur, with the locations of the greenish-white water seen near the coast (shaded). The lake is 7.7 km in the long dimension and has a surface area of 16 km2. Courtesy of CVGHM.

Figure 7. Photo of dead fish floating on the surface of Lake Batur associated with the fish kill of 2011. Thousand of fish died, many near the village of Toya Bungkah. Undated photo taken from indosurflife.com.

The translated report contained this important passage. "According to information from a resident (Made Yuni, age 59), the change in color of the lake water, consisting of patches of whitish green, is a yearly event, although [typically] small in scale and not causing the death of fish. The change in color of the lake water occurs during the change of seasons (i.e. the transition), between the wet and dry parts of the year when there is a stiff wind from the S. The incident of the lake water changing color and the death of the fish on 19 June 2011 occurred about two weeks into the dry season. The death of fish in Batur on the present scale happened before, in 1995."

Scientists conducted an examination during 21-22 June 2011. They also had pre-event temperature and pH for multiple sites on the lake going back at least several months. At the time of the visit, all residual odors had dispersed. Results of ambient gas measurements showed no traces of anomalous carbon monoxide, carbon dioxide, methane, or hydrogen sulfide. The lake temperature was found to be 15°C, which is considered normal. pH levels in the lake were found to be constant with other measurements taken in normal times as well. No increase in volcanic earthquakes were reported before or after the fish kill (the pattern of earthquakes was constant at typical background, 1 event/day). The colors seen were attributed to both warm water welling up (springs at Toya Bungkah) but also at places where such springs are absent.

On 20 June the water by the village of Seked returned to its normal color. Late in 21 June the water by the other villages involved returned to its normal color. Scientists found neither dead weeds or algae nor gas bubbles associated with the fish kill.

Cause of fish kill. Scientists from CVGHM found no evidence to conclude the fish kill was volcanically triggered nor did they mention it portending eruptive activity. Rather, the scientists noted the comparatively high diurnal-temperature difference during the onset of the dry season. As a result of these temperature differences, the lake water developed currents, which carried mud from the lake bottom to the surface. This was thought to correspond to the observed odors ('muddy smells') and color changes on the lake surface. In a broad sense, the currents and mud were thought to upset the lake's ecological balance in a manner toxic to the fish.

Residents were advised to not consume dead fish from the incident, but fish that had survived were still considered fit for human consumption.

Impactof fish kill. Many inhabitants around Lake Batur are fisherman by trade and it is estimated that the fish kill resulted in losses up to billions of Rupiah (1 billion Rupiah currently equivalent to ~ 120,000 US Dollars). The water of Lake Batur is also irrigated into surrounding farms. There is no official documentation on whether or not the recent events at Lake Batur have affected the neighboring agriculture.

Tectonic Setting

Rock Types

Population

Within 5 kmWithin 10 kmWithin 30 kmWithin 100 km

466,899
466,899
937,766
4,289,189

Geological Summary

The historically active Batur volcano is located at the center of two concentric calderas NW of Agung volcano. The outer 10 x 13.5 km wide caldera was formed during eruption of the Bali (or Ubud) Ignimbrite about 29,300 years ago and now contains a caldera lake on its SE side, opposite the satellitic cone of 2152-m-high Gunung Abang, the topographic high of the Batur complex. The inner 6.4 x 9.4 km wide caldera was formed about 20,150 years ago during eruption of the Gunungkawi Ignimbrite. The SE wall of the inner caldera lies beneath Lake Batur; Batur cone has been constructed within the inner caldera to a height above the outer caldera rim. The 1717-m-high Batur stratovolcano has produced vents over much of the inner caldera, but a NE-SW fissure system has localized the Batur I, II, and III craters along the summit ridge. Historical eruptions have been characterized by mild-to-moderate explosive activity sometimes accompanied by lava emission. Basaltic lava flows from both summit and flank vents have reached the caldera floor and the shores of Lake Batur in historical time.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Batoer | Bator | Molengraaff Caldera

Cones

Feature Name

Feature Type

Elevation

Latitude

Longitude

Abang, Gunung

Stratovolcano

2152 m

Anti, Gunung

Cone

1146 m

Bongkok, Bukit

Cone

1176 m

Bunder
Boender

Cone

1250 m

Butus, Gunung

Cone

Paleg

Cone

Pandan, Gunung

Cone

1140 m

Puraknja, Bukit
Poeraknja, Bukit

Cone

1156 m

Srongga, Bukit

Cone

1186 m

Craters

Feature Name

Feature Type

Elevation

Latitude

Longitude

Bunbulan

Crater

Catu
Tjatoe

Crater

1238 m

Goeha Songgadikit

Crater

1157 m

Payang
Pajang

Crater

Purakkanginan

Crater

Purakkauhan

Crater

Sampeanwani

Maar

1165 m

Tamansari Group

Crater

1179 m

Domes

Feature Name

Feature Type

Elevation

Latitude

Longitude

Bunbulan, Gunung

Dome

Songan

Dome

Photo Gallery

Batur volcano on the island of Bali was constructed within a 7.5-km-wide inner caldera whose SE margin is obscured beneath the foreground caldera lake, which fills part of the SE floor of an outer 10 x 13 km wide caldera. Batur stratovolcano was constructed as a result of eruptions along a NE-SW-trending line of vents. Historical lava flows have formed much of the far lake shore in this view.

Photo by Sumarna Hamidi, 1973 (Volcanological Survey of Indonesia).

Most of the extensive dark lava flows in the foreground were erupted during 1963-64 from vents near the Batur III cone on the lower SW flank of Batur stratovolcano, viewed here from the village of Penelokan, on the southern rim of Batur's outer caldera. The lava flows reached the caldera floor and destroyed 16 houses at Tamansari village. The complex stratovolcano was constructed within a 7.5-km-wide inner caldera. Activity has been concentrated along the NE-SW-trending chain of cones and craters seen cutting across the summit.

Photo by Sumarma Hamidi, 1973 (Volcanological Survey of Indonesia).

An aerial view overlooks Batur I, the summit crater of Batur volcano. Batur is a post-caldera stratovolcano constructed within the 7.5-km-wide Batur caldera. A chain of pyroclastic cones and craters was constructed along a NE-SW-trending line cutting through the summit. Historical eruptions have occurred from Batur I, Batur II, Batur III, and other flank cones.

Photo by Sumarma Hamidi, 1973 (Volcanological Survey of Indonesia).

A small ash eruption from Batur III cone on the SW flank of Batur volcano was photographed from the southern rim of Batur caldera in 1972. An ash eruption on January 19 was accompanied by strong explosions. Continuous ashfall was recorded from January 28 to February 12, and minor ash eruptions also took place in March.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).